lint and dust that collect inside kimono sleeves
Refers to the small debris that accumulates in the bottom of traditional Japanese sleeves (袂). A niche term mostly encountered in historical or cultural contexts.
着物を長く着ていると、袂糞がたまることがある。
When you wear a kimono for a long time, lint and dust can gather in the sleeves.
Compound of 袂 (たもと, 'kimono sleeve') and 糞 (くそ, 'excrement, waste'), literally 'sleeve waste'. The exact origin is uncertain, but it likely arose as a colloquial term for the debris that accumulates in the sleeve bottoms.